The present invention relates generally to electrical receptacles and more particularly to a banana type receptacle that is mountable on and positionable within a circuit board.
Banana type leads are used in the electronic industry for coupling signals to and from a device under test. A typical banana lead has a single wire terminated at each end with a male banana plug. The banana plug has an elongated conductive probe portion wrapped with a barrel spring, so that the probe portion may be inserted into a banana receptacle in an instrument. The banana receptacle has a conductive sleeve that makes contact with the barrel spring and is surrounded by electrically insulating material on the bottom and outer surface of the conductive sleeve.
Underwriters Laboratories, UL, has established insulation standards for electronic measuring and testing equipment (UL1244) that establishes minimum distances between conductive elements and users for preventing hazardous electrical shocks. Banana type leads that meet this standard have a tubular shaped shroud enclosing the male banana plug. The shroud is a thin walled cylinder of insulating material that provides the minimum distance separation between the male plug, coaxially disposed within the shroud, and the user. The corresponding banana receptacle may include an outer ring of insulating material defining an annular bore coaxial with the insulated conductive sleeve. The shroud of the male plug fits into the annular ring of the receptacle with the male plug making electrical contact with the conductive sleeve.
The conductive sleeve of the banana receptacle generally has electrical leads extending from the sleeve that are exposed at the bottom of the receptacle. The electrical leads are of a length that allows them to be inserted into electrically conductive apertures in a substrate, such as a circuit board. Conductive runs formed on the substrate couple the conductive apertures, and thus the conductive sleeve, to additional circuitry on the substrate. A particular problem with this type of banana receptacle is that the receptacle defines and controls the position of the circuit board in any hand-held electronic instrument design, and thus the overall design of the instrument. For example, the height of the receptacle defines the minimum thickness for the instrument for at least that portion of the instrument where the receptacle is positioned. A more complex shell design having differing surface levels is required if the instruments thickness is to be less than the minimum thickness associated with the receptacle. If, on the other hand, a flat surface shell is chosen, then the internal circuitry design may become more complex and expensive. For example, a custom display having a thickness matching the height of the receptacle may be required if the display is to be mounted directly onto the circuit board. Conversely, if the thickness of the display does not match the receptacle height, then conductive contact elements or cabling would be required for connecting the display to the circuit board which adds cost to the instrument. Likewise, buttons and knobs associated with most hand-held electronic instruments would be affected by the circuit board positioning problem.
An alternative to the above described receptacle-circuit board positioning problem is to remove the receptacles from the main circuit board. The receptacle or receptacles may be individually connected to the main circuit board via soldered wire connections between the receptacle leads and the circuit board. The receptacle or receptacles may also be bolted to the circuit board or instrument case with wire leads connecting the receptacle to the circuit board. The receptacle or receptacles may further be placed on a separate circuit board and electrically connected to the main circuit board via soldered wire connections between the leads of the receptacle(s) and the main circuit board or providing some form of interconnect between the boards. While this solution frees designers from the receptacle-circuit board positioning problem, it adds component and manufacturing costs to the instrument.
What is needed is an electrical receptacle, such as a banana receptacle, that is mountable on a substrate, such as a circuit board, without the limitations of previous receptacle-circuit board designs. The receptacle should not add component or manufacturing costs to the instrument and should be compatible with automated circuit board manufacturing processes. The receptacle should further be flexible to allow for positioning the circuit board anywhere within the shell of the instrument.